Pet Food Recalls and Pet Food Contaminants in Small Animals

Karyn Bischoff, DVM, MS a,b,*, Wilson K. Rumbeiha, BVM, PhD c

KEYWORDS

• Aﬂatoxin • Cholecalciferol • Cyanuric acid • Melamine

• Thiamine

• Vitamin B 1

• Vitamin D

Most pet foods are safe. Only 1.7% of reported poisonings in dogs and cats have been attributed to pet foods. 1Incidents of contamination occur through microbial action, mixing error, or intentional adulteration. Although rare, the effects of pet food contamination can be physically devastating for companion animals and emotionally devastating and ﬁnancially burdensome for their owners. Whereas most people consume a diet from various sources, for companion animals a single bag of food or cans from a single brand/lot will likely be the major or sole source of nutrition until that food has been completely consumed. Thus, the effects of food contaminants in people is diluted by the varied diet, but the uniform diet of most dogs and cats, although preferred for nutritional reasons, increases the risk of adverse effects if a contaminant is present in their food. As the companion animal veterinarian is aware, many animal owners consider their dog or cat to be a vulnerable family member that needs to be protected. 2Based on the authors’ experiences, pet owners often experience seemingly disproportionate guilt when pets become sickened or die after being unknowingly fed contaminated pet foods. Some owners have described feeling responsible for poisoning their pet during pet food contamination incidents. When pet food is contaminated or adulterated there is usually a food recall. There are 3 types of recalls involving chemical contaminants: Class I—reasonable proba- bility that the contaminated food will cause adverse health consequences or death; Class II—the contaminated food can cause temporary or medically reversible adverse

238 Bischoff & Rumbeiha health consequences but is unlikely to cause serious adverse health effects; and Class III—the contaminated food is unlikely to cause adverse health consequences. There were 22 Class I and II pet food recalls in the United States over a 12-year period (1996 to 2008), and 6 were due to chemical contaminants. 3Of these 6, 2 were due to aﬂatoxin (a mycotoxin), 3 were due to feed mixing or formulation errors (2 excess vitamin D 3and 1 excess methionine), and 1 was due to adulteration of food ingredients with melamine and related compounds. 3Since 2008, there have been 3 cat foods and 1 dog food recalled due to mixing or formulation errors (inadequate thiamine in the cat foods, excessive vitamin D 3in the dog food) and 1 dog and cat food recall due to contamination with aﬂatoxin. There have also been 2 US Food and Drug Administration (FDA) warnings and one from the Canadian Veterinary Medical Association since 2007 concerning a Fanconi- like renal syndrome in dogs after ingestion of large amounts of chicken jerky treat products, manufactured in China, over time. 4,5Similar warnings have occurred in Australia. 6Despite extensive testing, the cause of the adverse health effects (Fanconi-like syndrome) associated with consumption of chicken jerky has not been determined. Pet food contamination incidents due to adulteration are rare but occurred with melamine and cyanuric acid. The melamine contamination investigation in 2007 led to the discovery that other cases of melamine poisoning had happened in companion and agricultural animals in the Republic of Korea, Japan, Thailand, Malaysia, Singapore, Taiwan, the Philippines, South Africa, Spain, China, and Italy. 7–11There have been several other international pet food contamination incidents. Aﬂatoxin contamination of dog food has been mentioned in news stories from South Africa and Israel since 2006. The use of sulfur dioxide, which destroys thiamine, in processing pet foods has been associated with repeated outbreaks of polioencepha- lomalacia in dogs and cats in Australia. 12–14Also in Australia, there was a unique recall of irradiated cat food in 2008–2009, after it was found to cause severe central nervous system damage to cats. The proximate cause of the neurological disorder that afﬂicted cats fed irradiated pet food in Australia has not been determined to date. The FDA is charged with ensuring the wholesomeness of pet foods. The US Congress passed the FDA Amendments Act of 2007 (FDAAA) to improve responsive- ness to contamination of pet foods and other products after the adulteration of pet food with melamine and related compounds was identiﬁed that year. The FDAAA requires manufacturers to report incidents of possible contamination to the FDA within 24 hours, investigate the cause, and report ﬁndings of the investigation. When contamination is conﬁrmed, the pet food is recalled. Recall initiation is usually voluntary by the manufacturer at the request of the FDA. The FDA can secure a court order to issue a recall if the manufacturer is reluctant, but this is rare because of the bad publicity and increased potential for litigation should a manufacturer refuse to initiate a recall. 1Veterinarians must be involved for the FDAAA to work properly. This involves examining and treating animals that are suspected to have had adverse effects from pet foods, documenting pertinent ﬁndings, collecting appropriate samples, advising pet owners, and contacting the FDA and pet food manufacturers. Samples for laboratory analysis include the suspected food and its packaging (or, if unavailable, lot numbers, manufacturing codes, and other identifying information), and samples from the pet such as blood, serum, urine, vomitus or gastric lavage ﬂuids, and feces. A full necropsy with postmortem sample collection for histopathology and analytical chemistry includes fresh urine, adipose tissue, and heart blood, fresh and ﬁxed brain, liver, and kidney, and ﬁxed lung, spleen, and bone marrow. These samples are often

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required to rule in or out toxins when the affected animal dies or is euthanized. Often the pet food manufacturer will help with associated costs of treatment and testing; thus, it is in the interests of the pet owner and veterinarian to contact them as soon as contamination is suspected. Manufacturer contact information is usually found on product packaging. Consumer complaints can be reported to local FDA consumer complaint coordinators or online (http://www.fda.gov/cvm/petfoods.htm). Local gov- ernment agriculture or food safety agencies should also be alerted when contamina- tion of a commercial product is suspected. The rest of this text gives some details concerning major pet food contamination or formulation errors that have been associated with morbidity and mortality in pets in the United States, with mention of some minor contaminants and a formulation error that occurred in Asia. The most common natural contaminant of pet food is aﬂatoxin, a fungal metabolite. The common conditions that have been associated with misformulation include hypervitaminosis D and polioencephalomalacia. Last, in- cluded in the category of adulterants are melamine and related cyanuric acid.

NATURAL CONTAMINANTS

The most common natural contaminants in pet foods are mycotoxins (fungal metabolites). Aﬂatoxins are the most common mycotoxins to cause pet food recalls in the United States, but other mycotoxin contaminants have been reported. There was a recall of dog food due to contamination with the mycotoxin deoxynivalenol (DON) in 1995. DON is produced on grain by Fusarium spp under temperate conditions. Pet food DON concentrations of greater than 4.5 ppm and 7.7 ppm were associated with feed refusal in dogs and cats, respectively, and concentrations of 8 ppm or greater cause vomiting in both species. 15,16Animals recover quickly once the food is replaced, although supportive care is needed if gastroenteritis is severe. 16

Aﬂatoxin

Aﬂatoxicosis in dogs was ﬁrst described in 1952 as “hepatitis X” and reproduced in experimental dogs using contaminated feed in 1955, then by dosing with puriﬁed aﬂatoxin B 1in 1966. Moldy corn poisoning in swine in the 1940s and turkey X disease in turkeys fed peanut meal were also linked to aﬂatoxin. Aﬂatoxins are a group of related compounds sometimes produced as metabolites of various fungi, Aspergillus parasiticus, A ﬂavus, A nomius, some Penicillium spp, and others. Names of common aﬂatoxins are derived from the colors that ﬂuoresce:

aﬂatoxins B 1, the most common and potent form, and B 2ﬂuoresce blue and G 1and G 2both ﬂuoresce green. High energy foods, such as corn, peanuts, and cottonseed, are most often affected. Rice, wheat, oats, sweet potatoes, potatoes, barley, millet, sesame, sorghum, cacao beans, almonds, soy, coconut, safﬂower, sunﬂower, palm kernel, cassava, cowpeas, peas, and various spices can also be affected. 17,18Aﬂatoxin production can occur on ﬁeld crops or in storage. Temperature, humidity, drought stress, insect damage, and handling techniques inﬂuence mycotoxin pro- duction. 17Use of aﬂatoxin-contaminated food commodities in the manufacture of pet foods have caused intoxication in pets. Improper storage of dog food and ingestion of moldy garbage have been implicated in aﬂatoxicosis. 19Both dogs and cats are very sensitive to aﬂatoxin. 18The oral median lethal dose (LD 50) for aﬂatoxin in dogs is between 0.5 and 1.5 mg/kg. 20The experimental oral LD 50for cats is 0.55 mg/kg, although no ﬁeld cases of aﬂatoxicosis have been identiﬁed in cats to the authors’ knowledge. 18It is difﬁcult to determine the total dose of aﬂatoxin received in ﬁeld cases, where the period of exposure and amount fed are not always available. Aﬂatoxin concentrations of 60 ppb in dog food have been

240 Bischoff & Rumbeiha implicated in aﬂatoxicosis. 20Factors associated with increased susceptibility to aﬂatoxicosis include genetic predisposition, concurrent disease, age, and sex, with young males and pregnant females considered particularly susceptible. 20,21Aﬂatoxin is highly lipophilic and absorbed rapidly and almost completely, particu- larly in young animals, mostly in the duodenum. Aﬂatoxin enters the portal circulation and is highly protein bound in the blood. The unbound fraction is distributed to the tissues, with highest concentrations accumulating in the liver. 17The liver is the primary site of metabolism, although some metabolism takes place in other tissues, including the kidneys and small intestine. Phase I metabolism of aﬂatoxin B 1by cytochrome P450 enzymes produces the reactive intermediate aﬂatoxin B 18,9- epoxide. Some aﬂatoxin B 1is eventually metabolized to aﬂatoxin M 1. 21During phase II metabolism, aﬂatoxin B 18,9-epoxide is conjugated to glutathione in a reaction catalyzed by glutathione S-transferase. 22Metabolites of aﬂatoxin are excreted in the urine and bile, primarily as M 1in dogs. More than 90% of metabolized aﬂatoxin detected in canine urine is excreted within the ﬁrst 12 hours, and urine aﬂatoxin is below detectable concentrations within 48 hours. 23Conjugated aﬂatoxin is excreted mostly in bile. 17Aﬂatoxin B 18,9-epoxide, produced by metabolism of aﬂatoxin B 1, is a potent electrophile and binds readily to cellular macromolecules such as nucleic acids, proteins, and constituents of subcellular organelles. 24Formation of DNA adducts modiﬁes the DNA template and the ability of DNA polymerase to bind, affecting cellular replication, and binding to ribosomal translocase effects protein produc- tion. 20,25These changes can lead to necrosis in hepatocytes and, less frequently, other metabolically active cells such as renal tubular epithelium. 21Coagulopathy results from synthetic hepatic failure and decreased prothrombin and ﬁbrinogen. 26No carcinogenic effects have been reported in cats and dogs, although aﬂatoxins are known to be carcinogenic in some species, including rats, ferrets, ducks, trout, swine, sheep, and rats, and are classiﬁed by the International Agency for Research on Cancer (IARC) as Class I human carcinogens. 18,25The presentation of aﬂatoxicosis in small animals may be acute or chronic. Exposure to contaminated foods can occur for weeks or months before dogs become clinically affected; indeed, in one author’s experience, contaminated food was removed from the diet of a dog approximately 3 weeks before clinical aﬂatoxicosis was evident. Many dogs die within a few days of initial clinical signs, but illness can be protracted for up to 2 weeks. 21Early clinical signs of aﬂatoxicosis in dogs include feed refusal or anorexia, weakness and obtundation, vomiting, and diarrhea. Later, dogs become icteric, often with melena or frank blood in the feces, hematemesis, petechia, and epistaxis. 18,27Experimentally poisoned cats died within 3 days of onset of signs. 18Complete blood cell count, serum chemistry, including bile acids, and urinalysis are helpful to support the diagnosis of aﬂatoxin poisoning and rule out other causes of liver failure. Total bilirubin is increased in aﬂatoxicosis and hepatic enzyme concentrations, including alanine aminotransferase (ALT), aspartate aminotrans- ferase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transpeptidase (GGT), are variably elevated. 20,21Liver function tests are often more helpful in supporting the diagnosis. Prothrombin time is increased due to decreased synthesis of clotting factors, and serum albumin, protein C, antithrombin III, and cholesterol concentrations are decreased. 27Diagnosis of aﬂatoxicosis is usually based on history, clinical signs, clinical pathology ﬁndings, and postmortem changes. The primary differential diagnosis for dogs in recent food-contamination related cases of aﬂatoxicosis was often

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Fig. 1. Liver from a dog with aﬂatoxicosis. (Courtesy of S.P. McDonough.)

leptospirosis, but other differential diagnoses include parvovirus and anticoagulant rodenticide toxicosis based on the severe gastrointestinal hemorrhage, and a variety of hepatotoxic agents including acetaminophen, xylitol, microcystin from cyanobac- teria (blue-green algae), amanitin and phalloidin from mushrooms, toxins associated with cycad palms, phosphine, and iron. 20,27,28Necropsy is helpful in conﬁrming the diagnosis and ruling out other conditions. Common gross ﬁndings include icterus, hepatomegaly with evidence of lipidosis (Fig. 1), ascites, gastrointestinal hemorrhage, and multifocal petechia and ecchymosis. 20,26,27The primary histologic changes of canine aﬂatoxicosis are associated with the liver, although pigmentary nephrosis and necrosis of the proximal convoluted renal tubules have been reported. 21,26Liver lesions in acute toxicosis include fatty degeneration of hepatocytes with one to numerous lipid vacuoles. Centrilobular necrosis and canalicular cholestasis with mild inﬂammation are commonly reported. 19,26,27Dogs with subacute toxicosis still have fatty degeneration, canalicular cholestasis, and multifocal to locally extensive necro- sis, often with neutrophilic inﬂammation and evidence of regeneration. Fibrosis is more prominent, with bridging of portal triads, bile ductule proliferation, and obfus- cation of the central vein by dilated sinusoids. Chronic aﬂatoxicosis is characterized by less fatty degeneration, marked ﬁbrosis, and regenerative nodules, causing disruption of the normal hepatic architecture. 26Experimental cats with aﬂatoxicosis had hepatomegaly with petechiation, minimal hepatocystic glycogen storage, and, in cats surviving more than 72 hours, bile duct hyperplasia was also present. 18Laboratory testing of dog food or other implicated material helps to conﬁrm the diagnosis, but due to the extended time between exposure and onset of aﬂatoxicosis, the food is most often unavailable. Before the 2005 dog food recall, a veterinarian submitted dog food from each of 3 households, 2 of which had dogs with clinical aﬂatoxicosis, to a laboratory. The single sample that contained aﬂatoxin in toxicolog- ically signiﬁcant concentrations was from the household of a dog that had no clinical signs of toxicosis until weeks later. Commercial grain is routinely screened for aﬂatoxin, but sampling error is possible due to the uneven distribution of mold within the grain and other commodities. Current analytical techniques use enzyme-linked immunosorbent

242 Bischoff & Rumbeiha assays, high-performance liquid chromatography, and liquid chromatography/ mass spectrometry to detect aﬂatoxin. Some laboratories can test for aﬂatoxin M 1in the urine, but urinary excretion is very rapid in dogs. 23Urine may be useful for a period of up to 48 hours post exposure. Serum or liver can be tested, but due to the rapid metabolism and excretion of aﬂatoxin, this testing is often of limited usefulness. 20The prognosis for dogs with clinical aﬂatoxicosis is guarded. Early intervention improves the prognosis, but many cases fail to respond to treatment. 19,20,27Patient assessment and stabilization are the ﬁrst steps in management. Remove access to contaminated food and replace it with a high-quality protein containing diet if the dog continues to eat. Supportive care includes hydration and correcting electrolyte imbalances with intravenous ﬂuids, which can be supplemented with B vitamins, vitamin K, and dextrose. 21Plasma transfusions improve coagulation ability. 20Sucral- fate, famotidine, and sometimes parenteral nutrition have been used for anorexic dogs and those with severe gastroenteritis. 20,25Liver protectants, such as silymarin (a mix of silybin and other ﬂavolignans from milk thistle), have been used clinically and experimentally. When silymarin was given to chickens fed aﬂatoxin B 1in the diet, changes in liver enzyme proﬁles and histologic lesions were decreased compared to controls on clean diets. 24Proposed mecha- nisms of action for silybin include inhibition of phase I metabolism of aﬂatoxin B 1, thus decreasing epoxide production. 24,29S-Adenosylmethionine (SAMe), which can act as a sulfhydryl donor, has been used as a hepatoprotectant in aﬂatoxicosis cases. 20,27N-Acetylcysteine, a commonly used sulfhydryl donor, is given parenterally rather than orally for severely affected dogs. Experimentally, N-acetylcysteine (Mucomyst) has been shown to enhance elimination of aﬂatoxin B 1and prevent liver damage in poultry. 22MISFORMULATION As noted earlier, misformulation is a common cause of adverse reactions to pet foods in cats and dogs. Hypervitaminosis D and thiamine deﬁciency are discussed in detail later. Other misformulations have involved methionine, which caused a US recall, and excessive vitamin A in Thailand. Excessive methionine was associated with anorexia and vomiting. 3Misformulation of a feline research diet in Thailand in 2009 resulted in evident hypervitaminosis A (Dr Rosama Pusoonthornthum, personal communication, 2009). Hypervitaminosis A in cats and dogs causes osteopathy, commonly affecting the axial skeleton, and often presents as lameness, paresis, or paralysis due to entrapment of spinal nerves. 30,31Some animals with hypervitaminosis A, even those severely affected, recover in the long term after they are placed on a new diet. Hypervitaminosis D

Of the essential vitamins, vitamin D is the one that has been most frequently involved in pet food recalls. Vitamin D serves many physiologic roles, and regulation of calcium and phosphorous metabolism is one of the major roles. Other physiologic roles include immunomodulation and improved reproduction in animals. There are 2 major active forms of vitamin D in mammals. These are ergocalciferol (vitamin D 2) and cholecalciferol (vitamin D 3). There is also increasing use of 25-hydroxy vitamin D 3in animal feeds, particularly poultry and swine feeds. Oversupplementation and unin- tentional cross contamination have all caused vitamin D 3excess in pet food. There have been 3 pet food recalls triggered by excessive vitamin D 3in the past 15 years. In 1999, DVM Nutri-Balance and Golden Sun Feeds Hi-Pro Hunter dog food was recalled due to excessive amounts of cholecalciferol. In 2006, 4 products of ROYAL CANIN Veterinary Diet were recalled also due to excessive amount of

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cholecalciferol. More recently, in 2010, Blue Buffalo dog food was recalled due to contamination with 25-hydroxy vitamin D. Apparently this vitamin ingredient was intended for livestock feed, as it is not supposed to be used in the manufacture of dog food. HyD is a 25-hydroxy vitamin D product made for use in poultry feed, but there is inadequate information to determine the source of the 2010 pet food contamination with 25-hydroxy vitamin D. This incident, however, led to the discovery of a new phenomenon, the apparent physiologic interaction between 25-hydroxy vitamin D and cholecalciferol. The latter was present at recommended concentrations in the recalled dog food and yet clinically affected dogs had elevated serum ionized calcium and 25-hydroxy vitamin D and suppressed intact parathyroid hormone (PTH), all hallmarks of vitamin D toxicosis. In all these cases involving pet food, vitamin D poisoning occurred following prolonged ingestion of the contaminated food, usually weeks of exposure. Following ingestion, cholecalciferol is rapidly absorbed and transported to the liver where it is rapidly broken down to 25-hydroxy vitamin D 3. This is further metabolized primarily to 1,25-dihydroxy vitamin D 3(calcitriol) and 24,25-dihydroxy vitamin D 3in renal proximal convoluted tubular epithelium. Calcitriol is the vitamin D metabolite that is most important in calcium-phosphorus metabolism; thus, imbalances in these macrominerals are important to the pathophysiology of vitamin D toxicosis. Commonly reported clinical signs of vitamin D poisoning in pets include depres- sion, weakness, anorexia polyuria, and polydipsia. Often these are the only clinical signs noticed but are signiﬁcant enough to prompt pet owners to seek veterinary care for their pets. Diagnosis of vitamin D poisoning consists of clinical signs consistent with vitamin D poisoning and serum vitamin D toxicity proﬁle: serum intact PTH, total and ionized serum calcium, and serum 25-hydroxy vitamin D 3. In animals with vitamin D toxicosis, a signiﬁcant increase in serum calcium and phosphorus levels occurs and intact PTH is suppressed. In pets that have died, ﬁnding elevated 25-hydroxy vitamin D 3in the kidney, on top of histopathology characterized by metastatic soft tissue mineralization, is usually sufﬁcient to conﬁrm vitamin D poisoning. However, in cases of 25-hydroxy vitamin D poisoning, as in the case of Blue Buffalo recall, analysis for 25-hydroxy vitamin D 3could have been helpful, although reference values have yet to be established in dogs and cats. In episodes of vitamin D toxicosis triggered by pet food contamination, switching diets is often sufﬁcient to correct the problem. Patience is required, though, as it may take weeks before indices of vitamin D poisoning return to normal. Aggressive therapy includes use of salmon calcitonin, pamidronate disodium, corticosteroids, and furosemide diuretic among others. Treatment of vitamin D poisoning has been discussed more extensively elsewhere.

Thiamine Deﬁciency

As noted in the introduction, there have been 3 recent cat food recalls due to inadequate thiamine. Thiamine is a required B vitamin (B 1). Monogastric animals like cats and dogs cannot synthesize thiamine, and because it is a water-soluble vitamin, there is no long-term storage in the body. Factors such as age and diet affect the thiamine requirements for dogs and cats. 12Thiamine is absorbed predominantly in the small intestine via a carrier molecule. 32The vitamin is required as a coenzyme for pyruvate dehydrogenase, alpha-ketoglutarase, translocase, and other enzymes re- quired for carbohydrate metabolism and energy production. 12Pet foods should contain at least 5 mg/kg and 1 mg/kg thiamine on a dry matter basis, for cats and dogs, respectively. 13,33Thiamine deﬁciency in cats has been associated with a food containing 0.56 mg thiamine/kg dry matter. 34

244 Bischoff & Rumbeiha Thiamine is found in meat, liver, and some cereal grains. Causes of thiamine deﬁciency in small animals include feeding of meat preserved with sulfur compounds that cleave thiamine, cooking and processing, which destroys 40 to 50% of thiamine, and natural thiaminases found in raw ﬁsh. 12,14,34Absence of thiamine impairs cerebral energy metabolism, producing focal lactic acidosis and neuronal ischemia. 32,33Polioencephalomalacia describes the lesion associated with thiamine deﬁciency. Clinical signs described in experimental cats studied by Everett (1944) 35began after 2 to 4 weeks on the deﬁcient diet and included anorexia, which is responsive to thiamine injection, and weight loss. Progressive neurologic signs seen soon after included ataxia with a wide-based stance, circling, dilated pupils, positional ventro- ﬂexion of the head, and seizures, which may be spontaneous or secondary to stimulus. These signs remain responsive to thiamine supplementation. Eventually (after a month or more) cats become unable to walk and exhibit extensor tone in all limbs, which fails to respond to thiamine supplementation, followed by coma and death. 35Positional ventroﬂexion of the head, sometimes termed “the praying sign,” is active and caused by vestibular dysfunction rather than muscle weakness. This sign can be observed when the cat is held by the hindquarters and the front end is moved toward the tabletop. The chin will drop to near the sternum. 36Cats presented during the 2009 recall had similar clinical signs, including anorexia, head tilt, dilated pupils, apparent blindness, circling, ataxia, extensor rigidity of the front legs and positional ventral ﬂexion of the head, and seizures. All cats in the 2009 case were responsive to thiamine treatment except one with marked extensor rigidity. A study of puppies found that the ﬁrst signs occurred after nearly 2 months on a thiamine-deﬁcient diet and included inappetence, poor growth or weight loss, coprophagia, and neurologic signs similar to those seen in cats, although some puppies died before the abrupt onset of neurologic signs. 37Bilaterally symmetric changes have been observed in affected dogs and cats using magnetic resonance imaging, with lesions documented in the cerebellar nodulus, caudal colliculi, and periaqueductal grey matter, and in dogs the red nuclei and vestibular nuclei, and in cats the facial nuclei and medial vestibular nuclei. 14,33Diagnostic testing is infrequently used. Functional tests are considered sensitive indicators of thiamine deﬁciency. 32The most common is erythrocyte transketolase activity, which has been used in humans and dogs, but no reference values are available for cats. 12,32–34The reported thiamine pyrophosphate concentration is 32 g/dL in feline blood and 8.4 to 10.4 g/dL in blood from healthy canines. 37,38Cats in the 2009 outbreak had blood thiamine pyrophosphate concentrations ranging from 2.1 to 3.9 g/dL, but no samples from unaffected cats were analyzed. Postmortem lesions associated with thiamine deﬁciency–induced polioencepha- lomalacia in cats and dogs include bilaterally symmetric areas of petechia in the brainstem and elsewhere, corresponding to the areas seen on magnetic resonance imaging. Histologically, lesions include spongiform degeneration with reactive changes, including vascular hypertrophy, macrophage inﬁltrate, and gliosis. 12,37As noted previously, most animals respond to therapy with thiamine hydrochloride, given parenterally at a dose of 100 to 250 mg for cats and 5 to 250 mg/day for dogs. 39After 5 days of parenteral dosing in a cat, oral thiamine at 25 mg/d was continued for 1 month. 33Improvement is usually rapid, with signiﬁcant improvement observed within a few days and often complete within 1 to 12 weeks. 14,32,34,40However persistent, ataxia, hearing loss, and positional nystagmus are reported. 32,40

ADULTERATION

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Adulteration of pet foods is rare but was responsible for the largest pet food recall in US history. Melamine was intentionally added to pet food ingredients to enhance the apparent protein content. Protein in pet foods is estimated based on the nitrogen content, which is usually measured using the Kjeldahl method. Because melamine is 67% nitrogen based on the molecular weight, its addition to foodstuff increases the nitrogen content and thus the estimated protein content.

Melamine and Cyanuric Acid

Melamine, or 1,3,5-triazine-2,4,6-triamine, has found numerous uses in manufactur- ing. It can be used in yellow pigments, dies, and inks or can be polymerized with formaldehyde to produce a variety of durable resins, adhesives, cleansers, and ﬂame retardants. Cyanuric acid is an intermediate produced during melamine manufacture or degradation and is used to stabilize chlorine in swimming pools. Early in 2007, there were several reports of renal failure in cats and dogs consuming commercial pet foods in the United States. Clinical signs included inappetence, vomiting, polyuria, polydipsia, and lethargy. A large number of affected cats were on feeding trials at a laboratory. 41A recall was initiated on March 15 and melamine was detected in the cat food 2 weeks later, but at the time melamine was believed to have low oral toxicity based on early studies in rodents and dogs. Later, cyanuric acid, ammelide, and ammeline were detected. These are intermediates in the production of melamine from urea. The FDA investigation determined that wheat gluten and rice protein concentrates used in pet food production were intentionally mislabeled by Chinese exporters and actually contained wheat ﬂour and poor quality rice protein mixed with melamine. 10Eventually, more than 150 pet food products were identiﬁed, containing up to 3200 ppm melamine and 600 ppm cyanuric acid, and recalled. 41,42Samples of imported wheat gluten contained 8.4% melamine, 5.3% cyanuric acid, and 2.3% and 1.7% ammelide and ammeline, respectively. 3Estimates of the numbers of pets affected range from hundreds to thousands. Many consider the 2007 pet food recall a sentinel event. 10,43A year later, contamination of Chinese baby formula and other milk-based products was detected. Melamine concentrations ranged from 2.5 to 2563 ppm in 13 commercial brands of milk powder. 7More than 52,000 Chinese children were hospitalized and 6 died. There is evidence that children in Taiwan, Hong Kong, and Macau were also affected. 42,44,45Due to global marketing of food products and ingredients, melamine-contaminated foods were found in almost 70 countries, including the United States. The oral LD 50of melamine is 3200 mg/kg in male rats, 3800 mg/kg in female rats, 3300 mg/kg in male mice, and 7000 mg/kg in female mice. Long-term dietary administration of melamine to laboratory rats at concentrations ranging from 0.225% to 0.9% produced urolithiasis and urinary bladder lesions, including transitional cell carcinoma and, in females, lymphoplasmcytic nephritis and ﬁbrosis. 46Sheep were given single (217 mg/kg) or multiple (200 to 1,351 mg/kg/d for up to 39 days) doses of melamine. Clinical signs, including anorexia, anuria, and uremia, developed after 5 to 31 days after the ﬁrst exposure in a dose-dependent manner. 47A study involving dogs fed 125 mg/kg melamine reported crystalluria but no other adverse effects were identiﬁed. 48Cyanuric acid by itself has similarly low toxicity but is known to produce degenerative changes in the kidneys in guinea pigs at doses of 30 mg/kg body weight for 6 months, rats fed 8% monosodium cyanurate in the diet for 20 weeks, and in dogs fed 8% monosodium cyanurate in the diet. Lesions included ectasia of the distal collecting tubules and multifocal epithelial proliferation. 49The combination of

246 Bischoff & Rumbeiha melamine and cyanuric acid is markedly more toxic to most animals than either compound alone. Cats fed up to 1% melamine or cyanuric acid in the diet had no evidence of clinical abnormalities, but when fed diets containing 0.2% each of melamine and cyanuric acid, the cats had evidence of acute renal failure within 48 hours. Lesions were typical of those associated with the recalled pet food. 50A pig fed 400 mg/kg melamine and 400 mg/kg cyanuric acid daily had transient bloody diarrhea within 24 hours. Necropsy revealed perirenal edema and round golden-brown crystals with radiating striations in the kidneys. Similar lesions were present in tilapia, rainbow trout, and catﬁsh dosed with 400 mg/kg each of melamine and cyanuric acid daily for 3 days, although most survived the renal damage. 51Melamine and cyanuric acid form crystals in distal convoluted tubules of the kidney when given together by binding to form a lattice structure at pH 5.8. 7,10Renal pathology most likely results from intratubular obstruction and increased intrarenal pressure. Interestingly, cyanuric acid did not contribute to the formation of melamine- containing urinary calculi in children. 52Calculi in children were produced by a similar interaction between melamine and uric acid. Infants and many primates lack uricase, an enzyme that converts uric acid to allantoin and thus excrete uric acid via the kidneys. 51Urinary pH less than 5.5 is associated with the formation of urate crystals, and children with melamine/urate renolith formation were determined to have low urine pH. 52Melamine is minimally metabolized and does not accumulate in the animal body. It is about 90% eliminated within 1 day by the kidneys with a half-life for urinary elimination of 6 hours in dogs. 23,48Therefore, melamine should be almost completely excreted within 2 days; however, crystals were seen microscopically in feline kidneys 8 weeks after dietary exposure to melamine and cyanuric acid. 41Cats and dogs had evidence of renal failure after ingesting recalled foods. Clinical signs included inappetence, vomiting, polyuria, polydipsia, and lethargy. Urine speciﬁc gravities less than 1.035 and elevated serum urea nitrogen and creatinine concentrations were seen in these cats. Circular green-brown crystals were observed in urine sediment (Fig. 2). Postmortem examinations of animals that died or were

euthanized typically noted bilateral renomegaly and evidence of uremia. Microscopic lesions were primarily localized primarily to the kidneys: renal tubular necrosis, tubular rupture, and epithelial regeneration. In the distal convoluted tubules, there were large golden-brown birefringent crystals (15 to 80 m in diameter) with centrally radiating striations, sometimes in concentric rings, and smaller amorphous crystals. 41,53Crystals from kidneys and urine contained 70% cyanuric acid and 30% melamine based on infrared spectra. 10,53The outbreak of melamine-induced nephropathy in children differed from that in domestic animals by the absence of cyanuric acid. Uroliths associated with nephrotoxicosis in infants contained melamine and uric acid at a molar ratio of 1:1–2, respectively. 42,54Treatment regimens for crystalluria and urolithiasis related to melamine ingestion in veterinary and pediatric patients included ﬂuid therapy and supportive care. 54,55Oral and parenteral ﬂuid therapy increased urine output. Because low urinary pH is associated with crystal formation in infants, urine pH was maintained between 6.0 and 7.8 in affected children by adding sodium bicarbonate or potassium citrate to intravenous ﬂuids. Most children recovered with conservative management. 52,54Analysis of 451 cases matching the deﬁnition of melamine toxicosis found that 65.5% were cats and 34.4% were dogs. The case mortality rates were 73.3% and 61.5% for affected dogs and cats, respectively. Older animals and those with preexisting conditions were less likely to survive. 3However, more than 80% of exposed cats during the original feeding trials survived with supportive care. 41

SUMMARY

With myriad possible contaminants, ranging from fungal metabolites like aﬂatoxin and vomitoxin, to misformulations producing hypervitmaninoses and other nutritional excesses and deﬁciencies, to adulteration with industrial chemical such as melamine and related compounds, it is impossible to predict the cause of the next pet food recall. Indeed, the deﬁnitive cause of Fanconi syndrome in dogs associated with consumption of jerky treats for dogs has also not been found. Vigilance is our major line of defense.

ACKNOWLEDGMENTS

The authors would like to thank Drs Sanderson and Gluckman for their work with the aﬂatoxin dogs, Dr McDonough for his pathology work and for contributing Fig. 1, Drs Woosley and Hubbard for their work with the polioencephalomalacia cats, Dr Kang for his thiamine analysis, Dr Rosama Pusoonthornthum for information about hypervitaminosis A, and Dr Goldstein for his work with melamine-poisoned cats and for contributing Fig. 2.